The invention relates to a multi-lip drill, particularly a drill with three cutting lips, preferably for machining printed circuit boards, plastics or metals.
Multi-lip drills are also designated as multi-edge drills. The advantage of such drilling tools lies in the increased number of cutting edges and therefore in an increased drilling capacity, particularly in special materials.
It is known in drills that the size of the swarf flute is one determining factor of the feed pressure, that is to say a swarf flute of large cross-section in proportion to the cross-section of the drilling toll generates a lower feed pressure, because the swarf is eliminated with free mobility only to the extent of this flute cross-section. The region of the material to be removed in the bore in excess of the cross-section of the swarf flute has to be quasi additionally squeezed through the cross-section of the swarf flute. A large swarf flute can therefore discharge larger quantities of swarf for a lower feed pressure. However, for a lower feed pressure the cutting forces, and therefore the wear on the drilling tool, also remain low.
A multi-lip drill with an additional auxiliary flute, inserted in a principal swarf flute and oriented parallel thereto for the discharge of swarf is disclosed in German Patent No. 159,437, and more particularly, there is described therein a spiral flute which exhibits a second continuous flute. This second flute functions to permit an easier discharge of the swarf in spiral drills. To improve this function, it is proposed according to this German Patent that the auxiliary flute widens gradually from the tip towards the shank.
Further, German Auslegeschrift, [published patent application] No. 1,017,438 and French Patent No. 536,208 also disclose auxiliary flutes in the principal swarf flutes which, however, function to bend the swarf so that the latter breaks. No enlargement of the swarf space for easier discharge of the swarf is intended thereby.